The present invention relates to a projector and a distance measuring device which is suitable for equipment on a projector.
In these days, many data projectors are in use for projecting various types of images such as images displayed on screens of personal computers, images of video signals and, furthermore, images based on image data stored in memory cards on to screens.
In many such data projectors, a configuration is adopted in which a light source which is small in size and which has a high luminous intensity such as a metal halide lamp or an extra-high pressure mercury vapor lamp is used, light emitted from this light source is made into light rays of the three primary colors by a color filter and is then shone on to a liquid crystal or DMD (Digital Micromirror Device) display device via a light source side optical system, so that light that has passed through or been reflected on the display device is projected on to a screen via a group of lenses which is referred to as a projection side optical system having a zooming function.
In these projectors, there may be caused a situation where a trapezoidal distortion is generated in a projected image due to a distance between a screen and the projector, an inclination angle of the screen and a projection angle. Then, in order to correct such a trapezoidal distortion (a keystone distortion correction), it becomes necessary to measure accurately the distance between the screen and the projector, the inclination angle of the screen and the projection angle. To make this happen, a distance measuring device needs to be provided on the projector.
In the Japanese Unexamined Patent Application No. 2005-006228, for example, there is proposed a technique in which a distance measuring device for measuring distances to two points in a vertical direction and a distance measuring device for measuring distances to two points in a horizontal direction are disposed in the vicinity of a projection port, so as to calculate an inclination of a screen using the two distance measuring devices.
A distance measuring device on a general projector includes a light source, a photodetector or light receiving element and a light receiving lens, whereby light is emitted from the light source towards a distance measuring object, light reflected on the distance measuring object is made to be collected to the light receiving element by the light receiving lens, and the reflected light is made to be received by the light receiving element for calculation of a distance to the distance measuring object. In the distance measuring device, light reflected on the distance measuring object needs to be incident on the light receiving element in an ensured fashion. However, since a position where reflected light is collected by the light receiving lens deviates depending upon a distance to the distance measuring object, there is imposed a limitation on the distance of reflected light from the distance measuring object that can be received by the light receiving element, leading to a problem that the measurable range by the distance measuring device is limited.
In this way, in the distance measuring device of the conventional projector, the place to collect the reflected light from the distance measuring object changes, and this has sometimes made it difficult for such reflected light to be incident on the light receiving element. Because of this, in order to expand the range of incidence of reflected light on the light receiving element, there have been proposed several countermeasures such as increasing the size of the light receiving device, disposing a plurality of light receiving lenses or installing a reflection mirror in the vicinity of the light receiving element. However, these countermeasures call for an increase in size of the distance measuring device, and it has been difficult to install such an enlarged distance measuring device on a projector for which miniaturization has been demanded in these days.
Then, the present invention has been made in these situations, and an object thereof is to provide a small distance measuring device which can measure a distance accurately and which has a long measuring distance and a projector which includes this small distance measuring device.